1. Field of the Invention
The present invention relates to a device for changing operating force of a lens device, and in particular, to a device for changing operating force of a lens device capable of changing (adjusting) operating force (operating torque) for rotating an operating ring of an imaging lens used in a television camera and the like for broadcasting or business use.
2. Description of the Related Art
In a lens device used in a television camera for broadcasting or business use, there has been a well-known device including a rotatable operating ring provided around an outer periphery of a lens barrel, the device being capable of performing optical adjustment of an imaging optical system arranged in the lens barrel by manually or electrically rotating the operating ring. In a lens device called an ENG lens for a hand-held camera (an ENG camera) that is carried mainly in news gathering, and so on, for example, a focus ring for focus adjustment, a zoom ring for zoom adjustment, and an iris ring for diaphragm adjustment, are generally provided as the operating ring.
In a case where the operating ring above is manually rotated to perform optical adjustment, operating force (operating torque) required to rotate the operating ring affects an operational feeling of an operator, so that preferable operating torque to be felt differs depending on an operator. Thus, a mechanism of changing operating force, capable of adjusting operating torque of an operating ring, has been conventionally suggested as described in Japanese Patent Application Laid-Open Nos. 10-311939, 2005-84194 and 2000-258678, for example.
In Japanese Patent Application Laid-Open No. 10-311939, a thin plate member is arranged so as to be brought into sliding contact with an inner peripheral surface of an operating ring of a lens barrel. The thin plate member includes a mechanism of changing area of a region in which the thin plate member is in sliding contact with the inner peripheral surface of the operating ring by moving the thin plate member in an axial direction of the lens barrel with using a load adjustment knob. In addition, there is viscous fluid such as grease between the inner peripheral surface of the operating ring and the thin plate member. As a result, viscosity resistance of the viscous fluid applies a load against rotation of the operating ring to achieve an effect, such as that operating torque is reduced at a time of rotating at a constant low speed, and is increased at a time of rotating at a high speed. The mechanism of changing adjusts area of a region in which the thin plate member is in sliding contact with the inner peripheral surface of the operating ring so as to apply a load corresponding to area of a sliding contact region to the operating ring, thereby enabling a value of the operating torque to be adjusted.
In Japanese Patent Application Laid-Open Nos. 2005-84194 and 2000-258678, there is arranged a friction plate to be pressed a gear connected to a gear part of an operating ring. The friction plate includes a mechanism for changing pressing force to the gear. Accordingly, frictional force between the gear and the friction plate applies a load against rotation of the gear so that the load against rotation of the gear is applied as a load against rotation of the operating ring. An adjustment mechanism adjusts the pressing force of the friction plate to the gear to adjust a value of the frictional force (frictional resistance) between the friction plate and the gear, thereby enabling a value of operating torque of the operating ring to be adjusted.
An operating force adjustment device, such as shown in Japanese Patent Application Laid-Open No. 2002-107606, is suggested as a device of adjusting operating force in a lens operation by using viscosity resistance of viscous fluid. In Japanese Patent Application Laid-Open No. 2002-107606, the operating force adjustment device is connected to a cam barrel that drives a lens so as to adjust operating force required to rotate the cam barrel. The operating force adjustment device includes a casing for storing viscous fluid, and a rotary shaft supported by the casing, rotating in the viscous fluid, in which the rotary shaft includes a part extending to the outside of the casing external so that the part is connected to the cam barrel to rotate the rotary shaft together with rotation of the cam barrel. A rotary plate to be rotated in the viscous fluid is attached to a part of the rotary shaft in the casing, the rotary plate being rotated together with the rotary shaft, so as to apply viscosity resistance of the viscous fluid to the rotary shaft via the rotary plate. In addition, it is configured to apply desired voltage to the viscous fluid so that viscosity of the viscous fluid is adjustable by a voltage value of applied voltage. Accordingly, viscosity resistance of the viscous fluid against rotation of the rotary shaft of the operating force adjustment device is applied as a load against rotation of the cam barrel, serving as a load against an operation of rotating the cam barrel. Adjustment to viscosity of the viscous fluid by changing a value of voltage applied to the viscous fluid allows operating force for rotating the cam barrel to be adjustable.